1. Field of the Invention
This invention relates to a device and method for endovascular treatment of aneurysms, particularly cerebral aneurysms. The method and device fills the volume of the aneurysm, provides material to the locality of the treatment which contains pharmacologically active agents, and may use intrumentalities and materials which are visible with magnetic resonance so that the procedure may be viewed in real time with magnetic resonance imaging systems.
2. Background of the Art
Autopsy studies have estimated that between 1.5% and 8% of the population have intracranial aneurysms. Between 60,000 and 80,000 cerebral aneurysms are diagnosed annually in the U.S., 20,000 to 30,000 following subarachnoid hemorrhage. The annual risk of an aneurysmal rupture is about 2%, producing a mortality rate of 50-60%. If untreated, 25-35% die of recurrent hemorrhage and, if there is patient survival, there is a significant deficit in neurological functions in 20-40% of the patients.
The traditional method for detecting an aneurysm and evaluating its vascular relationships is cerebral angiography, which has a morbidity rate of 1-2%. Non-invasive angiographic techniques with minimal morbidity have been developed recently. Magnetic resonance (MR) angiography (MRA), a form of magnetic resonance imaging (MRI), and computed tomography (CT) angiography (CTA), have demonstrated very high levels of detection (60-100%, depending upon the size of the aneurysm and the technique used). In particular, MRI/MRA have been very effective in detecting the asymptomatic, unruptured aneurysms. Both MRA and CTA also might be excellent techniques for following patients after surgical treatment. Unfortunately, the materials used for treatment frequently degrade the image, making evaluation of residual or recurrent aneurysm difficult or impossible.
The traditional method of treating patients with ruptured and unruptured cerebral aneurysms is surgical clipping, and approximately 15,000 of these surgical procedures are performed in the U.S. each year. Surgical mortality from clipping a previously ruptured cerebral aneurysm varies from 5% to 20% to, depending upon the site of the aneurysm and the neurological condition of the patient at the time of surgery. Surgical mortality for an unruptured aneurysm is from 2% to 10%.
Because of this high surgical mortality rate, a number of endovascular techniques have been developed to treat cerebral aneurysms. In 1974, Serbinenko first reported the successful treatment of intracranial aneurysms with detachable balloons. Using an endovascular approach similar to an angiogram, the balloon would be directed under fluoroscopic guidance to the aneurysm. If possible, the balloon would be placed inside of the aneurysm, leaving the parent artery intact. If the neck of the aneurysm were too large to entrap the balloon completely inside of the aneurysm, occlusion of the parent vein or artery would have to be performed. Large aneurysms typically required multiple balloons. Since 1974, a variety of detachable and nondetachable balloons made of a variety of materials, especially silicone and biocompatible polymeric latices, have been introduced. However, most aneurysms do not have the round or elliptical configuration of a balloon. Consequently, large aneurysms had to be filled with multiple balloons, leaving dead space for continued aneurysmal filling and subsequent rupture. The unfilled volumes could also allow for the development of clot in the aneurysmal remnant, enabling embolization to produce a stroke. Migration of a balloon from the aneurysm into the parent artery, or to a more distal branch of the parent system to produce a stroke, has also been reported in the literature. The use of balloons for direct aneurysm occlusion is therefor no longer performed. Parent artery occlusion using a detachable balloon is still a viable procedure, although the blood flow to the hemisphere may be compromised with such a procedure, producing a stroke.
Aneurysmal occlusion with microcoils is another endovascular technique. Very soft platinum microcoils have been developed recently, with and without fibers that induce thrombus formation. These soft microcoils are placed directly into an aneurysm, and the degree of occlusion is related to the ability to pack the coil mass tightly. A new variety of microcoil is the Guglielmi Detachable Coil (GDC) (U.S. Pat. No. 5,122,136). This utilizes an electrical current to induce thrombosis within the aneurysm. The current also breaks the solder-point connection between the guiding wire and the coil for a non-forceful detachment of the coil. While the morbidity (8%) and mortality (0.3 to 1.1%) are very low with this procedure, especially compared to conventional surgery, the electrically induced intra-aneurysmal thrombus is lysed and the coils compact over time, so that the permanence and therapeutic efficacy of the aneurysm occlusion is still unknown. More importantly, complete occlusion of an aneurysm at the time of initial placement of the coils ranges from 69% for small aneurysms with narrow necks, to 35% or less for larger aneurysms with wide necks. Aneurysms having wide necks relative to their diameters may not be even treatable with this technique. A wide neck allows the coils to herniate into the parent artery, which may produce unwanted parent artery occlusion and stroke. Therefore, aneurysms with wide necks usually must be treated surgically, with a higher morbidity/mortality rate than if an endovascular method had been available. The GDC also produces undesirable artifacts on MR scans, making it impossible to define an aneurysmal remnant or tissue injury in the region of the aneurysm. Lastly, electrolytic detachment of the GDC can result in migration of the solder remnants into the intracranial circulation.
In order to completely fill the lumen of an aneurysm, a device with the properties of a liquid would be preferable to more rigid devices such as the GDC coil. Liquid agents have been used for aneurysm ablation by directly injecting the agent into the aneurysm to produce a cast and subsequent thrombosis. An example of a liquid thrombotic material is cellulose acetate and bismuth trioxide dissolved in dimethylsulfoxide. On contact with blood in the aneurysm, the dimethylsulfoxide diffuses and the concentrating cellulose acetate polymer solidifies in the shape of the aneurysm within minutes. The liquid thrombotic material has a low viscosity and is easily injected through a small gauge catheter placed into the aneurysm via an endovascular approach. However, there are significant problems with this method of aneurysm ablation, including the distal migration of the polymer into normal vessels, producing stroke, and the slow leaking of the chemicals into the blood with dispersion to normal brain tissue, producing neurological dysfunction.
Other liquids, especially the cyanoacrylates (e.g., the iso-butyl and n-butyl forms), have been used for aneurysm occlusion. The cyanoacrylates polymerize in seconds after making contact with an ionic fluid like blood. The polymerization rate is difficult to control, however, and its rapidity makes precise and safe placement difficult. Like any liquid, the cyanoacrylate can flow out of the aneurysm into unwanted locations unless it can be contained.
The guidance of an endovascular catheter system, and the placement of an embolic agent or device into an aneurysm, currently is performed using x-ray fluoroscopy. Catheters and embolic agents are made from radio-opaque materials to allow visualization, and fluoroscopy allows the real-time visualization of the movement of the catheter system and the placement of the intra-aneurysmal occluding agents. However, there would be certain advantages to performing such a procedure under MR guidance. First, x-ray systems give significant levels of radiation to the lens of the eye during aneurysm ablation procedures. Radiobiological effects such as cataract formation may prove to be significant once enough time has elapsed for the effect of these relatively new procedures to become known. MR does not utilize ionizing radiation, and there are no known long-term adverse effects on biological tissues from MR, as used in a clinical MR imaging environment.
Second, x-ray fluoroscopy is a two-dimensional imaging technique. Multiple projections must be used to totally understand the anatomy of an aneurysm and its neck. Three-dimensional reconstruction of two-dimensional angiographic data has been performed, but the computer processing times are long. MR angiographic data, however, can be processed quickly into a 3-D image, allowing the accurate analysis of the aneurysm, the luminal volume that must be filled, and the size of the neck that must contain the filling (embolic) agent.
Third, x-ray fluoroscopy and angiography permit visualization of only the blood vessels, not the brain substance itself. X-ray fluoroscopy does not allow the visualization of complications such as hemorrhage or stroke during aneurysm therapy, nor can physiological processes, such as cerebral perfusion, be studied during this procedure which may effect cerebral blood flow and perfusion. MR, however, is a powerful technique that permits visualization of blood vessels (with MRA), acute hemorrhage and stroke (with various pulsing sequences of MRI), and cerebral perfusion (perfusion MR). Newly developed fast MR sequences even permit MR fluoroscopy.
Therefore, it would be advantageous if the guidance of the catheter system and the intra-aneurysmal embolic agents could be performed by both x-ray and MR systems. This would require that the catheters, guidewires, and embolic agents be visible by both x-ray and MR or that different parts of a single system be visible by x-ray or MR. If the guidance system of catheters and guidewires and the aneurysmal occluding agent contained different elements that were visible with MR or with x-ray, the procedure could be performed on a hybrid MR/x-ray fluoroscopy system in order to take advantage of the features of both imaging systems. New technologies such as intra-operative magnetic resonance imaging and nonlinear magnetic stereotaxis (Gillies et al. 1994), as two examples, will likely play increasingly important roles in optimizing endovascular treatment of neurological disorders. One type of high-speed MR imaging system combines high-resolution MR imaging with conventional X-ray fluoroscopy and digital subtraction angiography (DSA) capability in a single hybrid unit. The real-time imaging capability of this combination of techniques makes it possible to use high-speed MR imaging to observe the effects of specific interventional procedures, such as thrombotic occlusion of aneurysms.
Visualization of an endovascular device could depend upon its being coated with an MR contrast agent, or upon its effect on the MR image by nature of its chemical makeup. However, compounds and materials considered MR compatible, and even MR contrast agents, can produce significant distortion artifacts that obscure the brain and blood vessel anatomy and physiology. Initial attempts to visualize endovascular devices in MR imaging were based on passive susceptibility artifacts produced by the device when exposed to the MR field. U.S. Pat. Nos. 5,154,179 and 4,989,608 to Ratner disclose the incorporation of paramagnetic material into endovascular devices to make the devices visible under MR imaging. However, these patents do not provide for artifact-free MR visibility in the presence of rapidly alternating magnetic fields, such as would be produced during echo-planar MR imaging pulse sequences used in real-time MR guidance of intracranial drug delivery procedures. Nor do these patents teach a method for monitoring with MR visible catheters the outcomes of therapeutic interventions. Ultrafast imaging sequences generally have significantly lower spatial resolution than conventional spin-echo sequences. Image distortion may include general signal loss, regional signal loss, general signal enhancement, regional signal enhancement, and increased background noise. The magnetic susceptibility artifact produced by the device must be small enough not to obscure surrounding anatomy, or mask low-threshold physiological events that have an MR signature, and thereby compromise the physician""s ability to perform the intervention.
An improved method for passive MR visualization of implantable medical devices has recently been disclosed by Werne (Pending U.S. patent application Ser. No. 08/554446, ITI Medical Technologies). That invention minimizes MR susceptibility artifacts, and controls eddy currents in the electromagnetic scattering environment, so that a bright xe2x80x9chaloxe2x80x9d artifact is created to outline the device in its approximately true size, shape, and position. In the method of the invention disclosed by ITI, an ultra thin coating of conductive material comprising 1-10% of the thickness of the material being imagedxe2x80x94typically about 250,000 angstromsxe2x80x94is applied. By using a coating of 2,000-25,000 angstroms thickness, ITI has found that the susceptibility artifact due to the metal is negligible due to the low material mass. At the same time, the eddy currents are limited due to the ultra-thin conductor coating on the device.
Exemplary of methods for active MR visualization of implanted medical devices is U.S. Pat. No. 5,211,165 to Dumoulin et al., which discloses an MR tracking system for a catheter based on transmit/receive microcoils positioned near the end of the catheter by which the position of the device can be tracked and localized. U.S. Pat. No. 5375,596 to Twiss et al., discloses a method for locating catheters and other tubular medical devices implanted in the human body using an integrated system of wire transmitters and receivers. U.S. Pat. No. 4,572,198 to Codrington also provides for conductive elements, such as electrode wires, for systematically disturbing the magnetic field in a defined portion of a catheter to yield increased MR visibility of that region of the catheter. However, the presence of conductive elements in the catheter also introduces increased electronic noise and the possibility of Ohmic heating, and these factors have the overall effect of degrading the quality of the MR image and raising concerns about patient safety. Thus, in all of these examples of implantable medical probes, the presence of MR-incompatible wire materials allows the possibility of causing large imaging artifacts. The lack of clinically adequate MR visibility and/or imaging artifact contamination caused by the device is also a significant potential problem for most commercially available catheters, microcatheters and shunts.
It is also important that endovascular devices used under MR guidance are MR-compatible in both static and time-varying magnetic fields. Although the mechanical effects of the magnetic field on ferromagnetic devices present the greatest danger to patients through possible unintended movement of the devices, tissue and device heating may also result from radio-frequency power deposition in electrically conductive material located within the imaging volume. Consequently, all exposed areas of the device, such as the cables, wires, surfaces and other devices positioned within the MR imaging system must be made of materials that have properties that make them compatible with their use in human tissues during MR imaging procedures.
A variety of implantable endovascular devices have been described, as follows:
U.S. Pat. No. 3,868,956 to Alfidi discloses a stent-like vessel expander or expandable filter made of a shape memory metal, such as an alloy containing nickel and titanium (Nitinol). An external woven (e.g., Dacron) sleeve is expanded by an internal Nitinol structure. The expansile appliance is initially formed in an expanded configuration and is then deformed to a straight-line configuration for implantation. Once placed in a desired position, the device is heated, causing it to resume its expanded configuration. In one embodiment, the appliance in its expanded configuration comprises a coil of wire used to expand or enlarge a vessel. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 4,503,569 to Dotter discloses the use of a coil of shape memory metal (Nitinol) as an endovascular stent. The endovascular prosthesis includes a helically wound coil having a generally tubular shape. After placement of the stent within a body blood vessel and upon heating of the prosthesis beyond 115 degrees C., it expands so as to become firmly anchored to the inside wall of the blood vessel. After expansion, the diameter of the lumen of the prosthesis is approximately equal to the diameter of the blood vessel. There is no reference to the application of this device for the treatment of cerebral aneurysms, nor is it MR visible.
U.S. Pat. No. 4,727,873 to Mobin-Uddin discloses an endovascular embolus trap, which is comprised of multiple filamentary loops extending outwardly from a central column. The device is inserted into blood vessels to engage and hold blood clots. Although obstructed vascular conditions are mentioned, there is no reference to applications for aneurysm therapy.
U.S. Pat. No. 4,994,071 to MacGregor discloses a bifurcating or branching stent in which a balloon expanding technique is used to expand the stent from insertion size to implant size. The balloon is then deflated and withdrawn from the vessel. Although obstructed vascular conditions are mentioned, there is no reference to applications for aneurysm therapy.
U.S. Pat. No. 4,998,539 to Delsanti discloses a method of using a removable device for promoting healing of detached flaps from the arterial wall. The expansile/contractile device is formed of interwoven wires. Remote actuation is used to cause expansion, and after healing, to cause contraction. It is thus distinguishable from the method and device of the present invention.
U.S. Pat. No. 5,035,706 to Gianturco discloses a specialized spring-expansible stent construction employing eyes formed at the bends of a zig-zag spring stent construction, as a variant of the Gianturco Z-form spring stent. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Ser. No. 07/788,799 to Clouse discloses a xe2x80x9cMethod and Device for Performing Endovascular Repair of Aneurysmsxe2x80x9d. However, the device is not specifically designed to be MR-visible.
U.S. Pat. No. 5,102,401 to Lambert et al. discloses an expandable catheter consisting of hydrophilic thermoplastic elastomeric polyurethane with a hydrophobic polymer coating. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,102,402 to Dror et al. discloses a balloon angioplasty catheter with a releasable drug-containing microcapsule coating on the balloon surface. However, device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,304,194 to Chee et al. discloses a vascular occlusion coil with multiple attached fibrous elements. However, the device is not specifically designed to be MR-visible.
U.S. Pat. No. 5,304,197 to Pinchuk et al. discloses a fabrication method for balloons as medical devices. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,304,199 to Myers discloses an elastomeric balloon for creating a cleft through a total blockage in a vascular structure. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,108,407 to Geramia et al. discloses a method and apparatus for placement of an embolic coil at an intravascular lesion site. The invention includes a heat sensitive adhesive to reversibly bond the coil to a connector. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,217,483 to Tower discloses an intravascular radially expandable stent. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,108,420 to Marks discloses an aperture occlusion device using a catheter-based wire occluder. However, the device is not MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,258,020 to Froix discloses a method of using an expandable polymeric stent with memory. However, the device is not MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,104,403 to Brotzu discloses a low porosity vascular prosthesis with hormone-producing cells contained within microcapsules placed in the walls of the prosthesis. However, the device is not MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,221,261 to Termin discloses a radially expandable intravascular fixation device and a method for securing the surface of the device to a tissue wall. However, the device is not MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,158,548 to Lau discloses a method and system for delivery of an expandable intravascular stent. However, the device is not MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,234,456 to Silvestrini discloses an intravascular stent with a semi-permeable membrane wall into which is placed a hydrophilic material capable of absorbing a liquid to increase the volume of the stent. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,234,457 to Anderson discloses an intravascular stent impregnated with a material that can initiate expansion of the stent into the vessel wall. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,342,303 to Ghaerzadeh discloses balloon catheters and related medical devices having non-occluding balloon inflation-deflation apertures. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,263,963 to Garrison discloses an expandable cage catheter for repairing a damaged blood vessel. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,330,500 to Song discloses a self-expanding endovascular stent with silicone coating. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,133,733 to Rasmussen discloses a collapsible filter for introduction into a blood vessel of a patient. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,037,427 to Harada discloses a method of implanting and removing an endovascular stent having a two-shape memory that is activated using a cooling liquid. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 4,994,069 to Ritchard discloses a vascular occlusion coil that uses a memory metal. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,370,691 to Samson discloses an intravascular polymeric inflatable stent. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,368,566 to Crocker discloses a temporary stent for maintaining blood vessel patency. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,378,239 to Termin discloses a radially expandable fixation device constructed of recovery metal. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,383,928 to Scott discloses a polymer stent sheath for local intravascular drug delivery. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,250,071 to Palermo discloses a detachable intravascular embolic coil assembly that uses interlocking clasps. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
U.S. Pat. No. 5,334,210 to Gianturco discloses a vascular occlusion assembly comprised of a bag of foldable material, and an internal catheter activator. However, the device is not specifically designed to be MR-visible.
U.S. Pat. No. 5,382,260 to Dormandy discloses an embolization device and apparatus including an introducer cartridge. However, the device is not specifically designed to be MR-visible.
U.S. Pat. No. 5,382,261 to Palmaz discloses a method and a tubular apparatus for occluding blood vessels. However, the device is not specifically designed to be MR-visible and there is no mention of using the device as an endovascular therapy for aneurysms.
A problem with the use of platinum microcoils, such as the GDC, is the lack of stimulation of scar formation within the aneurysm and an endothelial lining over the mouth of the aneurysm, insuring complete and permanent occlusion. U.S. Pat. No. 5,171,217 to March describes the delivery of several specific compounds by direct injection of microcapsules or microparticles using multiple-lumen catheters, such as disclosed by Wolinsky in U.S. Pat. No. 4,824,436. Incorporation of pharmaceutical agents into thin surface coatings during manufacture of a device will allow the agent to diffuse out of the coating at a controlled rate. The coating can incorporate natural or synthetic materials, such as antibiotics, thrombus-inducing or anti-thrombus chemicals, and agents such as fibroblastic and endothelial growth factors. U.S. Pat. No. 5,120,322 to Davis et al., describes the process of coating the surface layer of a stent or shunt with lathyrogenic agent to inhibit scar formation during reparative tissue formation, thereby extending exposure to the drug agent. U.S. Pat. Nos. 3,705,938 and 3,857,934 to the Herculite Protective Fabrics Corporation describe the incorporation of a chemical agent into a thin surface coating to allow diffusion of the chemical at a controlled rate.
However, exposed coatings on catheters which contain drug agents usually require some type of protective sheath that must be removed from the catheter before the drug can be released from the coating. The sheath and any catheter components required to manipulate the sheath greatly increase the profile of the catheter, make it less flexible, and thereby limit the variety of applications for which the drug delivery system can be employed, particularly for cerebral aneurysm treatment. In addition, binders or adhesives used in catheter coatings may significantly dilute the concentration of the therapeutic agent. The therapeutic agent could be bonded loosely to the catheter with a material such as macroaggregated albumin that is sensitive to thermal energy for release of the agent. U.S. Pat. No. 5,087,256 to Taylor describes an example of a catheter-based device that converts radiofrequency energy to thermal energy. However, the thermal energy required for release could cause damage to the blood vessel.
U.S. Pat. No. 5,470,307 to Lindall discloses a low-profile catheter system with an exposed coating containing a therapeutic drug agent, which can be selectively released at remote tissue sites by activation of a photosensitive chemical linker. In the invention disclosed by Lindall, the linker is attached to the substrate via a complementary chemical group, which accepts a complementary bond to the therapeutic drug agent. The drug agent is, in turn, bonded to a molecular lattice to accommodate a high molecular concentration per unit area. Ancillary compounds such as markers or emitters may also be attached to the drug agent so its location and movement can be monitored.
Another problem with current interventional therapies for treatment of cerebral aneurysms is the release of an embolic agent or device from the catheter transporting it to the aneurysm. The GDC platinum microcoil is attached to a transporting steel microguidewire by a small solder joint, and is detached when an electric current is passed through the steel microguidewire to lyse the solder joint. The time for this electrolytic release mechanism becomes progressively prolonged as more platinum coils are placed into the aneurysm. Detachable balloons, filled with either a fluid or a solid polymer, are detached when the transporting catheter is pulled back. The distended balloon exerts radial forces on the luminal walls of the aneurysm or blood vessel, and a special valve in the neck of the balloon closes as the catheter is withdrawn in order to keep the balloon distended. However, this technique exerts undo forces on the aneurysm, which may cause it to rupture. The direct placement of balloons into aneurysms, requiring such a release mechanism, is no longer performed. There is no other container to hold a polymerized fluid that could be placed inside an aneurysm, nor a mechanism to release such a container, in the current practice of endovascular therapy.
The present invention comprises a method and a device for treating hemodynamically significant aneurysms, particularly those of the intracranial circulation, while the procedure is being performed under image guidance mechanisms, especially either X-ray fluoroscopy and/or real-time magnetic resonance (MR) imaging guidance. A device for the practice of the present invention may comprise, for example, an association of a catheter and guidewire, a microcatheter, and a parachute element. A preferred construction comprises an association of a catheter and guidewire, a microcatheter, a parachute element, and a balloon. A preferred method of associating the respective elements would comprise having the balloon (if used) securely (less preferably detachably) attached to the catheter and the parachute element detachable from the microcatheter. The microcatheter may be carried through an opening in the balloon catheter, or may be separate, along the side of the balloon catheter, for appropriate placement during the procedure. Preferably the parachute element comprises an MR-visible, parachute-shaped device, containing a plurality of elongated filamentary loops made of flexible and expandable materials, such as an elastomeric hydrogel, polymeric materials such as polyamide mesh, Nitinol mesh (or a mesh of other biocompatible materials), or other expansile material. The parachute element, during the procedure, is radially expanded from a closed position while the device is within the lumen of the aneurysm. The device may be subsequently fixed, preferably permanently fixed, into surface contact with the aneurysm wall when the device is filled or partially filled with materials, such as a polymer material. MR visibility of the occlusive device is achieved using an MR-visible coating, filler, embedded elements or attachments within or on the composition of the device, permitting MR imaging of the device during and after the occlusion procedure. Detachment of the aneurysm occlusion device from the transport catheter, hollow wire, or hollow tube can be achieved by one or more of the following methods. The methods include, but are not limited to mechanical decoupling, hydration of the device/catheter or device/wire interface, by thermal exchange coupling or transduction, irradiation initiated change in adherent compositions, predetermined memory pH or osmolality changes, or by any other mechanical, chemical, electrical, and/or radiation techniques which can release the aneurysm occlusion device. The parachute device induces permanent occlusion of the aneurysm by timed delivery of biologic modifying drugs that promote fibroblast ingrowth and collagen formation within the aneurysm, and endothelial proliferation over the mouth of the aneurysm. The transporting microcatheter, the hollow tube or wire to which the parachute is attached, and the forming balloon catheter may have their surfaces impregnated with an MR-visible contrast material, or some other MR visible device may be attached to them. This will enable continuous MR visualization of their position during the filling of the parachute. The subject invention provides a method for the use of embolic materials under one or both of X-ray or MR-imaging guidance in ways different from those taught in the prior art.